A few caveats:

You will need cash. Most bars, restaurants, and shops in Berlin do not accept credit cards.
You will not be able to buy anything, including groceries, on Sunday. Stores in Berlin are closed on Sundays, but bars and restaurants are open.

Things to do:

Walking tours:

Insider Tour Berlin does the best walking tours in town. Those of you joining us for the walking tour on Friday, July 29 will be going on "The Famous Insider Walk." Their other tours are excellent as well, particularly Sachsenhausen, Potsdam, and Berlin Today: http://www.insidertour.com/

A day in Tiergarten, from west to east:

A day in Neukölln (home of Lauren and Flo):

Templehof Airport: Built in the 20s, reconstructed by the Nazis in the 30s, site of the Berlin Air Lift in the 40s. Today the airfield is a park and the Airport is a refugee camp. Go for a walk down the runways: https://en.wikipedia.org/wiki/Berlin_Tempelhof_Airport
Have a snack at this nearby brauhaus: http://www.doldenmaedel.de/
Nighttime kayak tour of Berlin: https://www.kajakberlintours.de/tours/night-tour/

A day in Treptower Park:

See Berlin's largest Soviet war memorial and cemetery: https://en.wikipedia.org/wiki/Soviet_War_Memorial_(Treptower_Park)
Walk over the Abteibrücke (Abbey Bridge) to the Insel der Jugend (Island of Youth): http://www.inselberlin.de/
Rent a canoe and go for a paddle on the Spree: http://www.kanuliebe.de/

Self-guided bike tour of Potsdam:

See Sanssouci Palace (favorite residence of Frederick the Great) and Cecilienhof (site of the 1945 Potsdam Conference). Pick up a bike and a map at the Griebnitzsee S bahn station: http://www.potsdam-per-pedales.com/bike-rental/

Olympic Stadium:

Those of you staying at Hotel Rotdorn will be staying right near the Olympic Stadium, site of the 1936 Summer Olympics (and more recently the final challenge on MTV's The Challenge: Battle of the Bloodlines): http://www.olympiastadion-berlin.de/en/stadium-visitor-centre/viewing-and-guided-tours.html

Museum Island:

Buy one ticket for all five museums on the island and make sure to see both the Egyptian collection (including the bust of Nefertiti) at the Neues Museum and the Classical Antiquities collection (including the Ishtar Gate of Babylon) at the Pergamon: http://www.smb.museum/en/museums-and-institutions/museumsinsel-berlin/home.html

Biergartens:

Cafe am Neuen See (a biergarten in Tiergarten): http://www.cafeamneuensee.de/
Prater (will be the last stop on the walking tour on Friday, July 29): http://www.pratergarten.de/e/index.php

Restaurants:

12 Apostel (best pizza in Berlin with locations in Charlottenburg and Mitte): http://www.12-apostel.de/
Barcomi's (best sandwiches in Berlin with locations in Bergmannkiez and Mitte): http://www.barcomis.de/index.php
The Bird (best burgers in Berlin with locations in Kreuzberg, Mitte, and Prenzlauer Berg, reservations recommended)
Dolden Mädel (a brauhaus near Tempelhof): http://www.doldenmaedel.de/
Sage Restaurant (a hip, industrial venue in Kreuzberg with an outdoor beach bar): http://www.sage-restaurant.de/cms_eng/restaurant

Near Hotel Rotdorn and the Grunewald:

Lakes:

Pools: